Understanding how the immature brain develops functional networks is a key challenge in neonatology. Analysis of functional MRI (fMRI) images acquired ‘at rest’ (rs-fMRI) allows inference of coordinated neural activity across disparate brain regions (functional connectivity (FC)). There is increasing interest in exploring neonatal brain development using rs-fMRI.
Most rs-fMRI work has focussed on fluctuations in blood oxygenation level dependent (BOLD) fMRI signals occurring at <0.2 Hz, despite neuronal fluctuations, as measured with electrophysiological means, occurring much more rapidly, leading to potential loss of crucial information about FC. This frequency limit has been influenced partly by the speed at which whole brain rs-fMRI acquisition can be accomplished. With typical fMRI protocols, the time taken to acquire each brain volume (repetition time, TR) is of the order of 2–3s. By Nyquist criterion, this means that ongoing BOLD fluctuations cannot be reliably sampled at frequencies above 0.2–0.25 Hz.
A method of improving rs-fMRI sampling frequency is ‘multiband’ parallel EPI, where multiple brain slices are excited simultaneously and spatially distributed receiver coils are used to encode anatomical data, allowing accelerated data reconstruction. We employed a rapid (TR = 906 ms) multiband rs-fMRI protocol to examine FC in 20 ex-preterm infants, probing BOLD fluctuations up to 0.5 Hz. We present power spectra, SNR data and comparisons of FC data at different frequencies, identifying unique functional changes at frequencies >0.2 Hz, which are not effectively identified within lower frequency fluctuations. This is the first description of multiband fMRI in neonates, and we discuss the implications for understanding infant brain networks.